The present invention relates to a motor brake device for controlling the drive of a motor.
As shown in FIG. 6, a conventional motor brake device for controlling the drive of a motor uses a brake release power supply to an electromagnetic brake which locks a motor shaft. The brake release power supply is formed by full-wave rectifying an AC power souse received through an insulating transformer.
Also in a power supply to a motor-drive indicator section, a voltage received from the insulating transformer is full-wave rectified, and the rectified one is formed into a constant voltage source by use of a capacitor, and the constant voltage source is supplied to the indicator section.
Contacts to synchronously turn on and off those two circuits must be provided for those circuits, respectively, since voltages supplied thereto are different from each other.
An AC power source 1 of a single phase is connected to an input side of an insulating transformer 2. AC powers of different voltages are supplied from the insulating transformer 2 to a motor-brake power supple circuit 3 and an indicator power supply circuit 6.
In the a motor-brake power supply circuit 3, a motor-brake release switch contact 3a is closed as needed, and a single-phase AC power is full-wave rectified by a bridge diode circuit 3b, and the rectified voltage is supplied to brake coils 4.sub.1 to 4.sub.n (n: number of existing coils) of an electromagnetic brake for locking the motor shaft, whereby the motor shaft is released from its locking state.
An indicator section 5 is provided for visually presenting a release of the motor brake to the operator.
The indicator power supply circuit 6 includes a switch contact 6a, which is operated synchronously with the motor-brake release switch contact 3a. When the switch contact 6a is closed, the single-phase AC power is full-wave rectified by a bridge diode circuit 6b, and the full-wave rectified power is further smoothed into a constant voltage by a capacitor 6c. The resultant constant voltage is applied to the indicator section 5, to thereby turn on the indicator section 5.
After seeing the lighting-on of the indicator section 5, the operator knows that the motor brake is released and the motor is in a driving state.
As described above, in the conventional motor brake device, the electric power is supplied, at different voltages, to the a motor-brake power supply circuit 3 and the indicator power supply circuit 6. For this reason, those power supply circuits are separately provided. Those circuits, respectively, include switch contacts for turning on and off the insulating transformer 2 (mainly used for voltage decreasing) and the bridge diode circuits 3b and 6b for full-wave rectifying. For this reason, the weight and size reduction is impossible.
In a trouble of poor contact in the switch contacts for synchronously turning on and off the power supply circuits, if one of the switch contacts is inoperative, an indication of the indicator section mismatches a driving state of the motor. As a result, the operator will be placed in a dangerous state.